Significant benefits can be derived from the ability to grow cells in vitro on biodegradable supports or scaffolds followed by transplantation to a human needing cells for tissue repair or replacement. Cells that could be grown for such tissue engineering include osteoblasts for new bone, chondrocytes for cartilage, fibroblasts for dermal tissue and retinal pigment epithelial cells (RPE) for the eye.
Some research regarding this aspect of tissue engineering has already been reported. For example, Mikos et al. have prepared poly(glycolic acid) bonded fiber structures for cell attachment and transplantation. J. of Biomedical Materials Research, Vol. 27, 183-189 (1993). Their preparations involved formation of a composite material between poly(glycolic acid) nonwoven fiber meshes and poly(L-lactic acid) (PLLA) followed by thermal treatment and selective dissolution of the PLLA matrix. Others have investigated porous sheets of polymer for such cell growth. Although the growth of cells on such porous film has been demonstrated, there are difficulties with such an approach.
The task of tissue engineering is complicated by the need of most cells to have special surfaces for attachment, proliferation and cell interactions. Additionally, some cells have distinctly different basal and apical characteristics and are polar in nature so that they function properly only when they are properly oriented.
There is a need, therefore, for a technique to develop and grow cells in vitro in a manner such that they will function properly when implanted. To this end, biodegradable polymers are needed to act as a scaffold or support for the development and growth of such cells. The scaffold should allow the growing cells to organize and develop special cellular function such as cell attachment, proliferation and maintenance of distinct basal and apical characteristics.
These needs are met by the present invention which provides a biodegradable scaffold for in vitro cell cultures, and a process for preparation of that scaffold. In particular, the biodegradable scaffold provides a suitable support for organization, proper attachment and growth of cells, especially those with special cellular functions.
In general, the invention is directed to the biodegradable scaffold which is composed of a filamentous porous thin film. The invention as well is directed to a process for preparing the filamentous porous film, and a method of using the filamentous porous film to provide a scaffold for cell growth and tissue engineering.
The filamentous, porous film can act as a support for cells to attach, grow and organize, including those with special functions and those requiring spatial orientation. The film has a matrix structure with two surfaces and is constructed primarily of filaments. The filaments define pores in the matrix structure. The pores extend from one surface to the other surface without a substantial change in the cross sectional dimensions of the pores. The filaments are composed of a pharmaceutically acceptable, biodegradable, thermoplastic polymer that is substantially soluble in a pharmaceutically acceptable organic solvent and substantially insoluble in aqueous medium and body fluid.
The mesh optionally contains at least one biologically active agent, which acts to enhance cell growth and/or tissue formation, or to prevent the growth of infectious agents, or to reduce pain and/or inflammation or, in the alternative, if drug delivery is contemplated, can act according to its recognized biological activity.
The process of the invention is carried out by applying liquid filaments of a flowable thermoplastic polymer solution onto an aqueous medium in such a manner that a solid filamentous porous film forms. By controlling the viscosity of the polymer solution and applying the polymer solution by any technique that forms droplets or small multiple volumes of the solution, the elongated small multiple volumes of solution, i.e., liquid filaments, can be formed which will result in the formation of a solid filamentous, porous film rather than a smooth, nonporous sheet.
The method of using the filamentous, porous film according to the invention involves use of the film as a scaffold for cell growth in a cell culture method.